you can go 4.25 stroke. using the big block chevy rods is a plus for crankcase clearance. steel rods give a little more clearance. the 470 i used to build had an offset ground 3.75 stroke steel mopar crank, bill miller 6.8 chevy alum rods, ross 12.5 pistons, stage 6 heads, program cross bolt main caps, and a half fill block. this was strictly a race engine and had an extremly reliable bottom end. the bob weight was close to stock 350 chevy. 2 years ago the engine recieved a 4.15 eagle crank (500 cubes), 12.5 je pistons, mopar bill miller 6.76, rods and indy ez heads. the 500 doesn't run a lick better than the old 470.